Difluro antivirals and intermediate therefor

ABSTRACT

A 2,2-difluoro-2-desoxycarbohydrate is used to prepare antiviral nucleosides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 07/449,156, filedDec. 15, 1989, now U.S. Pat. No. 5,015,743, which is a continuation ofapplication Ser. No. 07/288,383, filed Dec. 20, 1988, now abandoned,which is a division of application Ser. No. 07/058,219, filed June 4,1987, now U.S. Pat. No. 4,808,614, which is a division of applicationSer. No. 06/677,146, filed Dec. 4, 1984, now U.S. Pat. No. 4,692,434,which is a continuation-in-part of application Ser. No. 06/472,888,filed Mar. 10, 1983, now U.S. Pat. No. 4,526,988.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention belongs to the field of pharmaceutical chemistry, andprovides a new difluoro carbohydrate and new antiviral nucleosidesprepared by coupling the new carbohydrate with appropriate bases.

2. State of the Art

It has been known for some time that antiviral drugs can be found amongthe general family of nucleosides. For example,5-(2-bromovinyl)-2'-deoxyuridine is known to be a potent agent againstherpes virus DeClercq et al., Proc. Natl. Acad. Sci. USA 76, 2947-51(1979). Watanabe et al. have described a number of nucleosides formed bycoupling 2-fluoro-2-deoxyarabinofuranose with bases of the cytosine andthymine groups; 5-iodocytosine was their most preferred base. J. Med.Chem. 22, 21-24 (1979), and U.S. Pat. No. 4,211,773.

A compound which can be described as an acyclic nucleoside,9-(2-hydroxyethoxymethyl)guanine, is a potent antiviral agent,especially useful against herpes viruses, and is the subject of asymposium in a special issue of American Journal of Medicine, Jul. 1982.

Fluorinated carbohydrates have been studied before. A survey of thesubject by Penglis is in Advances in Carbohydrate Chemistry andBiochemistry 38, 195-285 (1981). A 2,2-difluorohexose was described byAdamson et al., Carbohydrate Research 18, 345-47 (1971). Wright andTaylor, Carbohydrate Research 6, 347-54 (1968), taught the synthesis of9-(3-deoxy-3-fluoroα-D-arabinofuranosyl)adenine.

Recently the total synthesis of carbohydrates has become the subject ofresearch, and a few papers have appeared. The synthesis requiresstereospecific methods, and asymmetric epoxidation and asymmetric aldolreactions have been successfully used. Masamune, Sharpless et al., J.Org. Chem. 47, 1373-81 (1982).

SUMMARY OF THE INVENTION

The present invention provides the difluorodesoxy carbohydrate of theformula ##STR1## wherein X is hydroxy or a leaving group; and the Ygroups independently are hydrogen or hydroxy-protecting groups.

The invention also provides the nucleosides of the formula ##STR2##wherein R is a base of one of the formulae ##STR3## wherein R¹ ishydrogen, methyl, bromo, fluoro, chloro or iodo;

R² is hydroxy or amino;

R³ is hydrogen, bromo, chloro or iodo.

The invention further comprises a process for preparing a lactone of theformula ##STR4## which process comprises hydrolyzing, under very mildconditions, an alkyl 3-dioxolanyl-2,2-difluoro-3-hydroxypropionate ofthe formula ##STR5##

Pharmaceutical compositions comprising a nucleoside of the above formulaand a pharmaceutically acceptable carrier, diluent or excipient thereforare provided as yet another aspect of the present invention, as is amethod of treating viral infections in mammals employing a present novelcompound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

All temperatures are described in degrees Celsius in this document.Liquids are reported in volume units.

The structural drawings above do not indicate the stereochemistry of thecompounds of the present invention. Compounds of all configurations arebelieved to be useful, and the stereochemistry of them is accordinglynot a limitation. However, it is preferred that the carbohydrate havethe configuration of naturally occurring ribose, as follows: ##STR6##

It is further preferred that the configuration of the juncture betweenthe ribose and the base be as follows: ##STR7##

It is believed that pharmaceutical chemists are aware of the bases whichare used in the synthesis of the antiviral nucleosides of the presentinvention, but the following specific nucleosides are mentioned toassure that every reader understands the type of antivirals which thisinvention makes available.

1-(5-methyl-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(5-bromo-2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(5-chloro-2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(5-iodo-2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(4-amino-5-chloro-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(4-amino-5-bromo-2-oxo-lH-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(4-amino-2-oxo-lH-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(4-amino-5-iodo-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(4-amino-5-methyl-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-[5-(2-bromovinyl)-4-hydroxy-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluororibose

1-[4-amino-5-(2-bromovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluororibose

1-[4-amino-5-(2-iodovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluororibose

1-[5-(2-chlorovinyl)-4-hydroxy-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluororibose

1-[4-hydroxy-5-(2-iodovinyl)-2-oxo-1H-pyrimidin-1-y]-2-desoxy-2,2-difluororibose

1-[4-amino-5-(2-chlorovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluororibose

1-(2-amino-6-oxo-1H,9H-purin-9-yl)-2-desoxy-2,2-difluororibose

1-(6-amino-9H-purin-9-yl)-2-desoxy-2,2-difluororibose

1-(5-fluoro-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(5-bromo-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(5-chloro-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(5-iodo-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(4-amino-5-fluoro-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

1-(4-amino-5-chloro-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(4-amino-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(4-amino-5-fluoro-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-(4-amino-5-methyl-2-oxo-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

1-5-(2-bromovinyl)-4-hydroxy-2-oxo-1H-pyrimidin-1-yl-2-desoxy-2,2-difluoroxylose

1-[4-amino-5-(2-bromovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluoroxylose

1-[4-amino-5-(2-iodovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluoroxylose

1-[5-(2-chlorovinyl)-4-hydroxy-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluoroxylose

1-[4-hydroxy-5-(2-iodovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluoroxylose

1-4-amino-5-(2-chlorovinyl)-2-oxo-1H-pyrimidin-1-yl]-2-desoxy-2,2-difluoroxylose

1-(2-amino-6-oxo-1H,9H-purin-9-yl)-2-desoxy-2,2-difluoroxylose

1-(6-amino-9H-purin-9-yl)-2-desoxy-2,2difluoroxylose

It will be understood that the reactions in which the novel2-desoxy-2,2-difluorocarbohydrate of this invention is coupled with thebases are frequently of a nature such that the hydroxy groups must beprotected to keep them from reacting with the base, or being decomposedin some manner. The protecting groups are chosen from the groups used insynthetic organic chemistry for the purpose. Chemists are accustomed tochoosing groups which can be efficiently placed on hydroxy groups, andwhich can be easily removed when the desired reaction is complete.Suitable groups are described in standard textbooks, such as Chapter 3of Protective Groups in Organic Chemistry, McOmie, Ed., Plenum Press,New York (1973); and Chapter 2 of Protective Groups in OrganicSynthesis, Greene, John Wiley & Sons, New York (1981).

Typical hydroxy-protecting groups include formyl, 2-chloroacetyl,benzyl, diphenylmethyl, triphenylmethyl, 4-nitrobenzyl, phenoxycarbonyl,t-butyl, methoxymethyl, tetrahydropyranyl, allyl, tetrahydrothienyl,2-methoxyethoxymethyl, methoxyacetyl, phenoxyacetyl, isobutyryl,ethoxycarbonyl, benzyloxycarbonyl and the like. Silyl hydroxy-protectinggroups are often particularly convenient, because most of them areeasily cleaved by contact with water or an alcohol. Such groups includeespecially trimethylsilyl, as well as isopropyldimethylsilyl,methyldiisopropylsilyl, triisopropylsilyl and the like. Thet-butyldimethylsilyl group is a special case and is preferred as theprotecting group in this synthesis; it is more difficultly cleaved andrequires a reagent such as a hydrohalic acid to remove it from thehydroxy groups.

Ribose or xylose has a hydroxy group at the 1-position of its ring. Inorder to react the carbohydrate of this invention with the base to formthe antiviral compounds of the invention, it is necessary to place aleaving group at the 1-position. The leaving groups used are typical ofthose used commonly in organic synthesis. The preferred leaving groupsare sulfonates, of which the most preferred is methanesulfonate; othertypical leaving groups such as toluenesulfonate, ethanesulfonate,isopropanesulfonate, 4-methoxybenzenesulfonate, 4-nitrobenzenesulfonate,and 2-chlorobenzenesulfonate. Chloro and bromo may also be used.

The following group of representative 2-desoxy-2,2-difluorocarbohydratesof the present invention are mentioned to assure the reader'sunderstanding.

2-desoxy-2,2-difluororibose

3,5-bis(trimethylsilyloxy)-2-desoxy-2,2-difluororibose

3,5-dibenzyloxy-2-desoxy-2,2-difluororibose

3,5-bis(chloroacetoxy)-2-desoxy-2,2-difluororibose

3,5-bis(2-chlorobenzyloxy)-1-methanesulfonyl-oxy-2-desoxy-2,2-difluororibose

3,5-bis(4-nitrobenzyloxy)-1-(4-toluenesulfonyl-oxy)-2-desoxy-2,2-difluororibose

1-chloro-3,5-bis(phenoxyacetoxy)-1,2-desoxy-2,2-difluoroxylose

1-(2,4-dibromophenylsulfonyloxy)-3,5-bis(2,2-dimethylpropionyloxy)-2-desoxy-2,2-difluoroxylose

3,5-bis(benzoyloxy)-1-(o-toluenesulfonyloxy)-2-desoxy-2,2-difluoroxylose

1-bromo-3,5-bis(methoxycarbonyloxy)-1,2-desoxy-2,2-difluoroxylose

3,5-bis(allyloxycarbonyloxy)-1-chloro-1,2-desoxy-2,2-difluoroxylose

3,5-bis(benzyloxycarbonyloxy)-2-desoxy-2,2difluoroxylose

1-bromo-3,5-bis(4-nitrobenzyloxycarbonyloxy)-1,2-desoxy-2,2-difluoroxylose

1-bromo-3,5-bis(tetrahydrothienyloxy)-1,2-desoxy-2,2-difluororibose

1-bromo-3,5-bis(isopropyldimethylsilyloxy)-1,2-desoxy-2,2-difluororibose

1-(2-chlorophenylsulfonyloxy)-3,5-bis(methoxymethoxy)-2-desoxy-2,2-difluororibose

3,5-bis(benzyloxymethoxy)-2-desoxy-2,2-difluororibose

1-(4-nitrophenylsulfonyloxy)-3,5-bis(trityloxy)-2-desoxy-2,2-difluororibose

3,5-bis(allyloxy)-1-chloro-1,2-desoxy-2,2-difluororibose

2-desoxy-2,2-difluoroxylose

3,5-bis(trimethylsilyloxy)-2-desoxy-2,2-difluoroxylose

3,5-dibenzyloxy-2-desoxy-2,2-difluoroxylose

3,5-bis(chloroacetoxy)-2-desoxy-2,2-difluoroxylose

3,5-bis(2-chlorobenzyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluoroxylose

3,5-bis(4-nitrobenzyloxy)-1-(4-toluenesulfonyloxy)-2-desoxy-2,2-difluoroxylose

1-bromo-3,5-bis(tetrahydrothienyloxy)-1,2-desoxy-2,2-difluoroxyose

1-bromo-3,5-bis(isopropyldimethylsilyloxy)-1,2-desoxy-2,2-difluoroxylose

3,5-bis(t-butyldiphenylsilyloxy)-2-desoxy-2,2-difluororibose

3,5-bis(formyloxy)-1-isopropylsulfonyloxy-2-desoxy-2,2-difluororibose

3,5-bis(trichloroacetoxy)-1-methanesulfonyl-oxy-2-desoxy-2,2-difluororibose

1-chloro-3,5-bis(phenoxyacetoxy)-1,2-desoxy-2,2-difluororibose

1-(2,4-dibromophenylsulfonyloxy)-3,5-bis(2,2-dimethylpropionyloxy)-2-desoxy-2,2-difluororibose

3,5-bis(benzoyloxy)-1-(o-toluenesulfonyloxy)-2-desoxy-2,2-difluororibose

1-bromo-3,5-bis(methoxycarbonyloxy)-1,2-desoxy-2,2-difluororibose

1-(2-chlorophenylsulfonyloxy)-3,5-bis(methoxymethoxy)-2-desoxy-2,2-difluoroxylose

3,5-bis(benzyloxymethoxy)-2-desoxy-2,2-difluoroxylose

1-(4-nitrophenylsulfonyloxy)-3,5-bis(trityloxy)-2-desoxy-2,2-difluoroxylose

3,5-bis(allyloxy)-1-chloro-1,2-desoxy-2,2-difluoroxylose

3,5-bis(t-butyldiphenylsilyloxy)-2-desoxy-2,2-difluoroxylose

3,5-bis(formyloxy)-1-isopropylsulfonyloxy-2-desoxy-2,2-difluoroxylose

3,5-bis(trichloroacetoxy)-1-methanesulfonyoxy-2-desoxy-2,2-difluoroxylose

3,5-bis(allyloxycarbonyloxy)-1-chloro-1,2-desoxy-2,2-difluororibose

3,5-bis(benzyloxycarbonyloxy)-2-desoxy-2,2-difluororibose

1-bromo-3,5-bis(4-nitrobenzyloxycarbonyloxy)-1,2-desoxy-2,2-difluororibose

The carbohydrates are prepared by a process beginning with the reactionof a D-glyceraldehyde ketonide of the formula ##STR8## wherein R⁴ and R⁵are independently C₁ -C₃ alkyl, with a C₁ -C₄ alkylbromodifluoroacetate, preferably the ethyl ester.

The preferred glyceraldehyde ketonide is the acetonide wherein R⁴ and R⁵are both methyl, which was first published by Fischer and Baer, Helv.Chim. Acta. 17, 622 (1934). Ethyl bromodifluoroacetate was firstprepared by Morel and Dawans, Tet. 33, 1445 (1977). The reaction of theketonide and the haloacetate is carried out in the presence of anactivated metal such as magnesium or preferably, zinc. The activation ismost easily obtained by applying ultrasonic energy to the reactionmixture. Activation by that means compensates for the presence of asmall amount of water in the reaction mixture, avoiding the necessity tomaintain anhydrous conditions, and also avoids the necessity to prepareand carefully store activated metals. However, the metal may beactivated by the customary methods used in the art if desired.Approximately an equimolar amount of metal is the most advantageousamount.

The reaction has been performed in ethers such as tetrahydrofuran anddiethyl ether, at moderate temperatures. However, other organic solventswhich are inert to the reaction conditions may be employed, includinghalogenated alkanes such as chloroform, dichloromethane, trichloroethaneand the like, and aromatics including such solvents as benzene, tolueneand the xylenes. Temperatures in the range of from about ambienttemperature to about 100° are convenient; temperatures from about theambient temperature to about 80° are preferred. Economically acceptableyields have been obtained in reaction times in the range of from a fewminutes to a few hours. It should be noted that the reaction isexothermic, and the mixture may therefore need to be cooled, dependingon the scale of the reaction and the rate at which the reactants areadded.

The product of the first reaction is an alkyl3-dioxolanyl-2,2-difluoro-3-hydroxypropionate of the formula ##STR9##

It appears that the ratio of the 3-R-hydroxy intermediate to its3-S-hydroxy enantiomer is about 3:1. The 3-R-hydroxy enantiomer has theproper stereochemistry to yield ribose in the natural configuration, andso it is the desired enantiomeric product of the first step. The3-R-hydroxy enantiomer can be cleanly separated from the 3-S-enantiomerby standard methods, for example by chromatography on silica gel,eluting with a solvent such as chloroform containing 0.5% methanol(v:v).

The hydroxypropionate, in either form, is hydrolyzed under very mildconditions to form the lactone form of the carbohydrate, of the formula##STR10##

It has been found that proper control of the hydrolysis step will cleavethe ketonide function and, unexpectedly, will also cleave the estergroup, providing the lactone in a single step. The hydrolysis reagent ispreferably a mildly acidic ion exchange resin, of which Dowex 50W-X12(Dow Chemical Company) is most highly preferred. It is possible to carryout the process with other mild hydrolytic reagents, although it ispossible that larger amounts of by-products may be obtained. Forexample, aqueous acetic acid, or other relatively strong acids such aspropionic acid, formic acid, chloroacetic acid, oxalic acid and thelike, may be used for the hydrolysis.

The hydroxy groups of the lactone should be protected before its ketooxygen is reduced. The usual reaction conditions are used, depending onthe nature of the protecting groups which may be chosen. For example,the t-butyldimethylsilyl group is most conveniently provided in the formof its trifluoromethanesulfonate, and the protection reaction is carriedout in the presence of a base such as lutidine, pyridine and the like.Acyl protecting groups such as acetyl, benzoyl and the like are providedby reacting the lactone with an acylating agent such as an acylchloride, bromide, cyanide or azide, or with an appropriate anhydride.The reactions are conveniently carried out in a basic solvent such aspyridine, quinoline or isoquinoline, or in a tertiary amine solvent suchas triethylamine, tributylamine, methylpiperidine and the like. Thereaction may also be carried out in an inert solvent, to which an acidscavenger, such as a tertiary amine, has been added. Acylation catalystssuch as 4-dimethylaminopyridine or 4-pyrrolidinopyridine may be used inthe reaction, if desired. The acylation reactions which provideprotecting groups on the hydroxy groups are carried out at moderatetemperatures in the range of from -25° to 100°. Such acylations may alsobe performed by acid-catalyzed reactions of the appropriate carboxylicacids, in inert organic solvents or neat. Acid catalysts such assulfuric acid, polyphosphoric acid, methanesulfonic acid and the likeare used.

Acyl protecting groups may also be provided by forming an active esterof the appropriate acid, such as the esters formed by such knownreagents as dicyclohexylcarbodiimide, acylimidazoles, nitrophenols,pentachlorophenol, N-hydroxysuccinimide and 1-hydroxybenzotriazole.

Protecting groups of the ether type are placed by reacting the lactonewith, for example, an appropriate diazo compound, such as diazomethane,phenyldiazomethane or a silyldiazomethane. Such reactions are commonlyand effectively carried out in solvents including esters such as ethylacetate, halogenated solvents including dichloromethane and chloroform,and ethers including diethyl ether and tetrahydrofuran. The process isusually carried out at low temperatures from about -50° to about 0°.Such ether-forming reactions may also be carried out with the assistanceof reagents such as trimethyloxosulfonium hydroxide, trimethylsulfoniumhydroxide and trimethylselenonium hydroxide, in solvents such asdimethylsulfoxide, dimethylformamide, hexamethylphosphoramide, acetone,acetonitrile and the like.

The silyl protecting groups discussed above are placed on the hydroxygroups by the conventional methods, such as by reaction with theappropriate silylcarboxamide or bis(substituted-silyl)carboxamide, or anappropriately substituted silazane. Suitably substituted silylmethanesulfonates, toluenesulfonates and the like are also useful. Anequivalent of a base is usually necessary in the reaction mixture,unless a basic solvent such as is discussed above is used as thereaction medium.

When the hydroxy groups have been protected, the keto oxygen of thelactone is reduced to the alcohol, forming the protected2-desoxy-2,2-difluororibose or xylose of this invention. The mostpreferred reducing agent is diisobutyl aluminum hydride, used at a lowtemperature in the range of about -100° to -20°. It is necessary tocarry out the reduction very carefully, in order to avoid reducingconditions so vigorous that the ring is opened at the oxygen atom. Othermetal hydrides, such as the widely used lithium aluminum hydride, canalso be used for the reduction, but it is necessary to keep thetemperature quite low and to assure that the hydride is destroyed beforethe temperature is allowed to rise toward ambient. Accordingly, asolvent with a very low freezing point must be used in the reductionstep. Toluene is convenient; other solvents can of course be used,including lower alkanols, especially ethanol, ethers such as diethylether, and the like.

An appropriate leaving group must be placed at the 1-position of thecarbohydrate, in order to obtain efficient reaction with the base. Thepreferred leaving group is methanesulfonyl, which is readily provided byreaction with methanesulfonyl chloride in the presence of an equivalentamount of a suitable acid scavenger such as triethylamine and the like.Other sulfonyl leaving groups are provided in the same way by reactionwith the appropriate sulfonyl halide.

When a chloro or bromo leaving group is to be used, it is frequentlyconvenient to first make the 1-acetate derivative, for instance byreaction with acetic anhydride, or another source of acetyl groups, inthe presence of an equivalent or more of an acid scavenger. Then theacetate group is displaced with gaseous hydrogen bromide or hydrogenchloride, at a low temperature such as about -50° to about 0°. Since thegaseous hydrogen halide may tend to remove the protecting groups,especially silyl protecting groups, it is necessary to operate this stepat quite a low temperature and to add the hydrogen halide slowly insmall increments.

The bases used to form the antiviral compounds of the present inventionare commonly known to organic chemists, and no discussion of theirsynthesis is necessary. However, the primary amino groups which arepresent on some of the bases should be protected before the base iscoupled with the carbohydrate. The usual amino-protecting groups areused, including silyl groups such as have been discussed, as well assuch typical groups as t-butoxycarbonyl, benzyloxycarbonyl,4-methoxybenzyloxycarbonyl, 4-nitrobenzyloxycarbonyl, formyl, acetyl,and the like.

It is often advisable to convert keto oxygen atoms on the bases to theenol form, in order to make the bases more highly aromatic and therebyallow more ready attack of the base by the carbohydrate. It is mostconvenient to enolize the oxygens by providing silyl protecting groupsfor them. The usual silyl protecting groups as discussed above are usedfor this purpose, also.

The reaction between the protected carbohydrate and the base ispreferably carried out neat at an elevated temperature in the range offrom about 50° to about 200°. It is possible, however, to use relativelyhigh-boiling solvents for the reaction, such as dimethylformamide,dimethylacetamide, hexamethylphosphoramide and the like. However, if thecoupling reaction is carried out under elevated pressure, to avoiddistillation of a low-boiling solvent, any convenient inert reactionsolvent can be used.

The coupling reaction may be done at low temperatures if a reactioninitiator, such as a trifluoromethanesulfonyloxysilane, is used. Theusual inert reaction solvents, as discussed above, may be used attemperatures in the range of from about ambient to about 100°.

The final step of the reaction sequence is the removal of the protectinggroups. Most silyl protecting groups are easily cleaved by contact withwater or an alcohol. The t-butyldimethylsilyl protecting group requiresacid conditions, such as contact with gaseous hydrogen halide, for itsremoval.

Acyl protecting groups are removed by simple hydrolysis with strong ormoderately strong bases, such as alkali metal hydroxides, attemperatures from about the ambient temperature to about 100°. At leastone equivalent of base is needed for each protecting group, of course.Such hydrolyses are conveniently carried out in hydroxylic solvents,especially aqueous alkanols. The reactions may be also carried out,however, in any convenient solvent, such as polyols including ethyleneglycol, ethers such as tetrahydrofuran and the like, ketones such asacetone and methyl ethyl ketone and other polar solvents such asdimethylsulfoxide. The cleavage of acyl protecting groups may also beperformed with other bases, including, for example, sodium methoxide,potassium t-butoxide, hydrazine, hydroxylamine, ammonia, alkali metalamides and secondary amines such as diethylamine and the like. The acylprotecting groups can also be removed with acid catalysts, such asmethanesulfonic acid, hydrochloric acid, hydrobromic acid, sulfuricacid, or with acidic ion exchange resins. It is preferred to carry outsuch hydrolyses at a relatively high temperature, such as the refluxtemperature of the mixture, but temperatures as low as ambient may beused when particularly strong acids are used.

The removal of protecting groups which are ethers is carried out byknown methods, for example, with ethanethiol and aluminum chloride.

None of the reaction steps require unusual excesses of the reactants. Asusual in organic syntheses, it is advisable and economical to use amoderate excess, in the range of 1.05× to 2×, for example, of thecheaper reagents to assure that the costlier ones are consumed.

The following preparations and examples further illustrate the synthesisof compounds of the present invention.

PREPARATION 1 ethyl2,2-difluoro-3-hydroxy-3-(2,2-dimethyldioxolan-4-yl)propionate

To 10.2 g. of activated zinc was added a small portion of a solutionconsisting of 31.8 g. of ethyl bromodifluoroacetate and 22.6 g. of4-formyl-2,2-dimethyldioxolane in 53 ml. of tetrahydrofuran and 53 ml.of diethyl ether. Care was taken to exclude water from the reactionmixture. The solution began to reflux as soon as the first addition tothe activated zinc was made. The remainder of the solution was addeddropwise at a rate to maintain gentle reflux throughout the additiontime of about 30 minutes. The mixture was then stirred under gentlereflux for 30 minutes more. The reaction mixture was poured into 200 ml.of 1N hydrochloric acid and 200 g. of ice, and the mixture was stirreduntil all of the ice had melted. The aqueous mixture was then extractedfour times with 70 ml. portions of diethyl ether, and the organic layerswere combined and washed with 50 ml. of saturated aqueous sodiumchloride and with 50 ml. of saturated aqueous sodium bicarbonate, driedover magnesium sulfate and evaporated under vacuum to obtain 26 g. oflight yellow oil. The crude product was chromatographed on a 1000 g.silica gel column, eluting with chloroform containing 0.5% methanol toseparate the major 3-R-hydroxy product from the minor 3-S-hydroxyproduct. The ratio of amounts of the two products was about 3:1; theminor product came off the column first.

Evaporation of the fractions containing the 3-R-hydroxy product provided12.6 g. of the product in substantially pure form. It was identified bymass spectrometry, showing a fragment of weight 239, which agrees withthe molecular weight of the desired product less a methyl group whichwas lost from the acetonide function in the spectrometric measurement. Anuclear magnetic resonance analysis of the 3-R-hydroxy product on a 90MHz instrument in CDCl₃ showed features at δ=3.94-4.45 (m, 5H); 3.14 (d,J=4.5Hz, 1H); 1.2-1.47 (m, 9H).

Analysis by the same nmr procedure of the 3-S-hydroxy product, of which4.68 g. was obtained by evaporation of the chromatography fractionscontaining it, showed features at 3.75-4.47 (m, 6H); 2.95 (d, J=8Hz,1H); 1.25-1.5 (m, 9H).

PREPARATION 2 2-desoxy-2,2-difluoro-1-oxoribose

Fifty g. of the 3-R-hydroxy product obtained from a synthesis similar tothat of Preparation 1 above was dissolved in 500 ml. of methanol and 250ml. of water, and 250 g. of Dowex 50W-X12 resin was added. The mixturewas stirred at ambient temperature for 4 days, and the mixture was thenfiltered through a pad of diatomaceous earth filter aid. The filtratewas evaporated to dryness under vacuum to obtain 33.0 g. of the desiredproduct, which was identified by nmr analysis on a 90 mHz instrument inCD₃ OD: δ=3.6-4.6 (series of m, 4H); 4.8 (bs, 2H).

PREPARATION 33,5-bis(t-butyldimethylsilyloxy)-2-desoxy-2,2-difluoro-1-oxoribose

To 13 g. of the product obtained in Preparation 2 above was added 60 ml.of dichloromethane, 22.5 ml. of 2,6-lutidine and 48.2 ml. oftrifluoromethylsulfonyloxy t-butyldimethylsilane under nitrogen withmild cooling to keep the temperature below 25°. Within 15 minutes aftercombining the reagents, the reaction became quite exothermic and themixture became thin and easily stirred. The mixture was stirredovernight. The mixture was diluted with 150 ml. of ethyl acetate, andwas washed successively with 40 ml. of 1N hydrochloric acid, 40 ml. ofsaturated aqueous sodium bicarbonate and 40 ml. of saturated aqueoussodium chloride. It was then dried over magnesium sulfate and evaporatedto dryness under vacuum to obtain 32.1 g. of crude product, which waschromatographed on 260 g. of 100-mesh silica gel, eluting with 10:1(v:v) chloroform:diethyl ether. The fractions which contained thedesired product were combined and evaporated under vacuum to obtain 7.8g. of pure product. Other fractions were combined and evaporated toobtain an additional 10 g. of impure product, which was not furtherpurified. Analysis of the pure product gave the following results: IR(neat) 1820 cm.⁻¹ ; nmr (CDCl₃, 90 MHz) δ=0.1-0.22 (m, 12H); 0.83-0.98(m, 18H); 3.63-4.7 (series of m, 4H); mass spec. m/e=339=P-t-butyl.

EXAMPLE 1 3,5-bis(t-butyldimethylsilyl)-2-desoxy-2,2-difluororibose

A 10.3 g. portion of3,5-bis(t-butyldimethylsilyloxy)-2-desoxy-2,2-difluoro-1-oxoribose,obtained from preparations similar to that of Preparation 3 above, wasdissolved in 120 ml. of anhydrous toluene and cooled to -84°. To thesolution was added 26 g. of diisobutyl aluminum hydride, added over aperiod of 20 minutes with constant stirring. The reaction mixture washeld below -65° at all times. Two hours after the first addition ofhydride, the reaction mixture was quenched with methanol at -20°,additional cold methanol was added until no more gassing occurred. Themixture was then allowed to warm slowly to ambient temperature, and waswashed with 100 ml. of 0.1N hydrochloric acid. The aqueous layer wasthen washed with 100 ml. of diethyl ether, and then three times with 50ml. portions of diethyl ether. The organic layers were combined, washedwith 100 ml. of saturated aqueous sodium bicarbonate, dried overmagnesium sulfate and evaporated under vacuum to dryness to obtain 8.2g. of the desired product in crude form.

This material may be chromatographed, if necessary, on silica gel (25 g.silica/1 g. of crude product) using 100% dichloromethane for elution.nmr (CDCl₃, 90 MHz) δ=0.1-0.24 (m, 12H); 0.85-1.0 (m, 18H); 3.33-4.63(series of m, 5H); 5.0-5.27 (dd, 1H); mass spec. m/e=341=P-t-butyl;[α]_(D) ²⁵° =25.1°.

EXAMPLE 23,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororibose

An 0.5 g. portion of3,5-bis(t-butyldimethylsilyloxy)-2-desoxy-2,2-difluororibose wasdissolved in 5 ml. of anhydrous dichloromethane and 0.17 g. oftriethylamine. To the solution was added, with mild cooling, 0.11 ml. ofmethanesulfonyl chloride. After three hours of stirring under nitrogenat about 25°, the mixture was evaporated under vacuum, and the residuewas taken up in 10 ml. of ethyl acetate. The solution was extracted with3 ml. of saturated aqueous sodium bicarbonate, and then successivelywith 3 ml. of 1N hydrochloric acid, 3 ml. of water and 3 ml. ofsaturated aqueous sodium chloride. The organic solution was then driedover sodium sulfate and concentrated under vacuum to obtain 0.59 g. ofthe desired product, nmr (CDCl₃, 90 MHz) δ0.05-0.16 (m, 12H); 0.78-0.90(m, 18H); 3.0 (s, 3H); 3.63-4.59 (series of m, 4H); 5.67-5.9 (dd, 1H);mass spec. m/e=419 =P-t-butyl.

EXAMPLE 31-(5-methyl-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

To 2.59 g. of3,5-bis(t-butyldimethylsiloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororibosewas added 1.60 g. of 5-methyl-2,4-bis(trimethylsilyloxy)pyrimidine and45 ml. of dry 1,2-dichloroethane. To this mixture was added 1.45 g. oftrifluoromethanesulfonyloxytrimethylsilane, and the clear solution wasstirred under nitrogen at reflux for about 2-3 hours. The reaction wasthen cooled to ambient temperature and 1.35 ml. of methanol were addedand the suspension was stirred for 30 minutes. The precipitate wasfiltered and the filtrate was reduced to one-half its volume undervacuum and then diluted with an equal volume of dichloromethane. Thesolution was washed with saturated aqueous sodium bicarbonate and thenwith saturated aqueous sodium chloride, and dried over anhydrous sodiumsulfate. The solution was filtered and the filtrate was saturated withanhydrous hydrogen bromide. The reaction mixture was stirred for 30minutes and was then concentrated under vacuum. The residue wasdissolved in methanol and the solution was evaporated to dryness undervacuum. The residue was dissolved in water and the solution wasextracted twice with diethyl ether. The water layer was then evaporatedto dryness. The residue was taken up in ethanol and evaporatedrepeatedly to azeotrope off all water. One g. of crude product wasobtained, and was chromatographed on 30 g. of Woelm silica gel (70-150mesh), eluting with ethyl acetate to yield 0.76 g. of desired product.It was further purified by recrystallization from ethyl acetate toobtain 0.37 g. of white crystalline product. nmr (CD₃ OD, 90 MHz) δ1.93(s, 3H); 3.5-4.67 (series of m, 4H); 4.83 (bs, 3H); 6.3 (t, J=9Hz, 1H);7.47 (m, 1H); mass spec. m/e=278=Parent.

EXAMPLE 41-(5-methyl-2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

A 5.4 g. portion of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororiboseand 5.4 g. of 5-methyl-2,4-bis(trimethylsilyloxy)pyrimidine werecombined and heated under nitrogen with stirring at 100° for one hour,and then at 150° for one hour. The mixture was then cooled to ambienttemperature and diluted with 25 ml. of water and 10 ml. of methanol. Theslurry was filtered over a diatomaceous earth filter pad, and the cakewas washed with acetone. The combined filtrate was evaporated undervacuum to obtain 5.3 g. of an oily residue. The residue was dissolved in10 ml. of acetone and loaded on a 4.5 cm. column packed with 80 g. ofsilica gel. It was eluted with 15:1:1dichloromethane:methanol:triethylamine.

The first 100 ml. of eluent was discarded, and the next 300 ml. wasevaporated under vacuum to obtain 4.1 g. of syrupy crude product, whichwas dissolved in 40 ml. of acetone. Hydrogen chloride was bubbledthrough the solution for 1 hour, and then hydrogen bromide was bubbledthrough for 1 hour more. The solution was then evaporated at 62° toobtain 4.4 g. of oily dark product.

The above product was dissolved in 10 ml. of warm 3:1dichloromethane:acetic acid, and loaded on a 4.5 cm. column packed with45 g. of silica gel. The eluent used for the first 1000 ml. was 3:1dichloromethane:acetic acid, and thereafter it was acetic acid alone.Most of the desired product was in the fractions between 1000 and 1400ml. off the column, as determined by thin layer chromatography on silicagel using 15:1 dichloromethane:methanol. Those fractions were combinedand evaporated under vacuum, and the residue was taken up in 15 ml. ofcold acetone and filtered. The filtrate was stripped under vacuum toobtain an oi, which was dissolved in 5 ml. of acetone andchromatographed over 20 g. of silica gel with 15:1dichloromethane:methanol. The product-containing fractions were combinedand evaporated under vacuum to obtain 300 mg. of a semi-solid. Thatproduct was taken up in 5 ml. of acetone and filtered, and the filtratewas evaporated under vacuum to obtain 230 mg. of light brown semi-solid.It was dissolved in 10 ml. of saturated aqueous sodium bicarbonate, andthe solution was extracted twice with 15 ml. portions of diethyl ether.The aqueous phase was then evaporated under vacuum, the residue wasslurried in acetone and filtered, and the filtrate was evaporated undervacuum to obtain 140 mg. of the desired product as a tan viscous oil.

The following example illustrates a preferred method of isolating acompound of the present invention.

EXAMPLE 51-(5-methyl-2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

To 80.0 g. of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororiboseunder a nitrogen atmosphere was added 1.4 1. of freshly distilledmethylene chloride and 49.5 g. of5-methyl-2,4-bis(trimethylsilyloxy)pyrimidine. To this mixture was added44.8 g. of trifluoromethanesulfonyloxytrimethylsilane and the reactionmixture was refluxed for approximately 31/4 hours. The reaction mixturewas stirred at room temperature overnight and 41.6 ml. of methanol wasadded thereto. The resulting mixture was stirred for approximately 30minutes and the precipitated solid was collected by filtration. Thefiltrate was concentrated under vacuum at 45° to provide a dark oilwhich was dissolved in 500 ml. of methylene chloride saturated withanhydrous hydrogen bromide. The resulting suspension was stirred forapproximately 3 hours after which the volatiles were removed undervacuum at 45°. The residue was dissolved in 100 ml. of 10% sodiumbicarbonate and 100 ml of diethyl ether. The aqueous layer was separatedand concentrated in vacuo at 50° to provide a residue which wastriturated three times with 100 ml. portions of hot ethyl acetate. Theorganic layers were combined and evaporated under vacuum at 45° toprovide a residue which was dissolved in 50 ml. of water. This solutionwas chromatographed in 10 ml. portions on a Waters Prep 500 C¹⁸ reversephase column using water/methanol (v:v, 9:1) as the eluent to provide2.21 g. of1-(5-methyl-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose.nmr (CD₃ OD, 90 NHz) δ1.9 (s, 3H), 3.65-4.65 (m, 4H), 4.83 (s, 3H), 6.12(dd, J=7Hz, 12Hz, 1H), 7.70 (s, 1H); mass spec. m/e=278=p.

EXAMPLE 6 1-(5-iodo-2-oxo-4-amino-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

To a solution of 1.99 g. of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororibosein 35 ml. of dry methylene chloride under a nitrogen atmosphere wasadded 2.08 g. of tris (trimethylsilyl)-5-iodocytosine and 1.11 g. oftrifluoromethanesulfonyloxytrimethylsilane. The reaction mixture wasrefluxed for approximately 16 hours and cooled to room temperature. Fivemilliliters of methanol were added to the mixture which was stirred forapproximately 30 minutes. The precipitated solid was collected byfiltration and the filtrate was evaporated to dryness under vacuum. Theresidue was dissolved in 20 ml. of methylene chloride saturated withanhydrous hydrogen bromide to provide a suspension which was stirred forapproximately 3 hours at room temperature. The volatiles were evaporatedunder reduced pressure at 45° and the resulting residue was dissolved in15 ml. of water. The solution was neutralized to a pH of approximately 7to 8 with 10% sodium bicarbonate and washed one time with 10 ml. ofethyl acetate. The aqueous layer was chromatographed on a Whatman PrepODS-3 reverse phase column in 2 ml. portions employing water/methanol(v:v, 9:1) as the eluent to provide 30 mg. of1-(5-iodo-2-oxo-4-amino-lH-pyrimidin-1-yl)-2-desoxy-2,2-difluororibosenmr (CD₃ OD, 90 MHz) δ3.47-4.66 (m, 4H), 4.78 (s, 4H), 6.14 (2e, J=7Hz,1H), 8.32 (s, 1H); mass spec. m/e=389=p.

EXAMPLE 71-(5-fluoro-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

A solution of 1.1 g. of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororibose,0.83 g. of 5-fluoro-2,4-bis(trimethylsilyloxy)pyrimidine, and 0.655 g.of trifluoromethanesulfonyloxytrimethylsilane in 20 ml. of methylenechloride was refluxed for approximately 17 hours under nitrogen. Thereaction mixture was cooled to room temperature and 3 ml. of methanolwas added thereto. The resulting solution was stirred for approximately30 minutes at room temperature and the precipitated solid was collectedby filtration. The filtrate was evaporated to dryness under vacuum at50° and the residue was dissolved in 15 ml. of methylene chloridesaturated with anhydrous hydrogen bromide. The resulting suspension wasstirred for approximately 30 minutes and the volatiles were removed invacuo at 45°. The residue was dissolved in 15 ml. of water and theaqueous solution was extracted one time with 10 ml. of ethyl acetate.The aqueous layer was neutralized with sodium carbonate to a pH ofapproximately 7 and the solution was evaporated to dryness in vacuo at50°. The residue was dissolved in about 6 ml. of water and the resultingsolution was chromatographed in 2 ml. portions on a Whatman ODS-3 50cmreverse-phase column using water as the eluent to provide 30 mg. of1-(5-fluoro-2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose. nmr (CD₃ OD, 90 MHz) δ3.63-4.6 (m, 4H), 4.79 (s, 3H),6.04 (t, J=7 Hz, 1H), 8.07 (d, J=6 Hz, 1H); mass spec. m/e=282=p.

EXAMPLE 81-(2-oxo-4-amino-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

Under nitrogen, to a solution of 47.3 g. of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororibosein 940 ml. of methylene chloride was added 48 g. ofbis(trimethylsilyl)-N-acetylcytosine. To this mixture was added 39.23 g.of trifluoromethanesulfonyloxytrimethylsilane and the resulting mixturewas stirred under reflux for approximately 15 hours. The reactionmixture was cooled to room temperature and 16 ml. of methanol was addedthereto. The resulting solution was stirred for approximately 30 minutesand concentrated to about one-half of its original volume. The solutionwas cooled in ice and the precipitated solid was collected byfiltration. The filtrate was shaken one time with approximately 300 ml.of 10% sodium bicarbonate and one time with 100 ml. of brine. Theorganic layer was evaporated to dryness in vacuo at 45° and the residuewas dissolved in 1.3 1. of methanol saturated with ammonia. Theresulting suspension was allowed to stir overnight at room temperatureand the volatiles were removed under vacuum at 45°. The residue wasdissolved in 275 ml. of methanol and 100 g. of Bio Rad ion exchangeresin (AG 50WX8) was added thereto. The suspension was stirred at roomtemperature overnight and the resin was collected by filtration. Theresin was rinsed with 100 ml. of methanol and suspended in 100 ml.methanol and 50 ml. of concentrated ammonium hydroxide. The resincontaining suspension was stirred vigorously for 15 minutes and theresin was collected by filtration. This procedure was twice repeatedwith additional ammonia saturated methanol. The basic methanolicfiltrates were combined and evaporated at 45° under vacuum to provide13.8 g. of a solid. This material was chromatographed on a Waters Prep500 _(C) ¹⁸ Reverse Phase Column with water as the eluent to provide1.26 g. of1-(2-oxo-4-amino-lH-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose. nmr(CD₃ OD, 90 MHz) δ3.7-4.65 (m, 4H), 4.83 (s, 4H), 5.97 (d, J=8 Hz, 1H),6.24 (t, J=7 Hz, 1H), 7.88 (d, J=8 Hz, 1H); mass spec. m/e =263=p.

EXAMPLE 91-(2-oxo-4-amino-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluoroxylose

Under nitrogen, to 23 g. of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluoroxylosewas added 23 g. of tris(trimethylsilyl)cytosine and 300 ml. of methylenechloride. To this mixture was added 10.84 g. oftrifluoromethanesulfonyloxytrimethylsilane and the mixture was refluxedfor approximately 16 hours. The mixture was cooled to room temperatureand 20 ml. of methanol was added thereto. The solution was stirredvigorously for approximately 1 hour at room temperature and theprecipitated solid was collected by filtration. One hundred millilitersof water were added to the organic layer and the suspension was stirredvigorously for 30 minutes. The organic layer was separated andevaporated to dryness under reduced pressure to provide 11.2 g. of abrown oil. The residue was dissolved in 97 ml. of methanol to which 33g. of Bio Rad AG 50X8 cationic exchange resin was added. The suspensionwas stirred for approximately 16 hours at room temperature and the resinwas collected by filtration. The resin was washed with 50 ml. ofmethanol and stirred vigorously in a solution of 100 ml. of methanol and100 ml. of ammonium hydroxide. This procedure was twice repeated and thecombined filtrates were concentrated under vacuum at 50° to provide 2.09g. of a yellow residue. The residue was suspended in 25 ml. of water andstirred vigorously for 15 minutes. The insoluble precipitate wascollected by filtration to provide 0.25 g. of a substance labelledCompound A. The filtrate was concentrated in vacuo at 50° to provide0.86 g. of a compound labelled B. Compound A was dissolved in 20 ml. ofmethanol and stirred for 3 days with Bio Rad AG 50WX8 at ambienttemperature. The resin was filtered and slurried in 30 ml. of a 1:1, v:vsolution of methanol/ammonium hydroxide. The resin was again filteredand the filtrate was concentrated in vacuo at 50° to provide 0.14 g. of1-(2-deoxy-2,2-difluoro-β-D-xylofuranosyl)cytosine. nmr (CD₃ OD, 90 MHz)δ3.72-4.34 (m, 4H), 4.78 (s, 4H), 5.86 (d, J=8 Hz, 1H), 6.17 (d, J=15Hz, 1H), 7.78 (d, J=8 Hz, 1H); mass spec. m/e=263=p.

The compound labelled B was chromatographed on a Whatman 50cm ODS-3Reverse Phase Prep column using water/methanol (v:v, 1:1) as the eluentto provide 0.06 g. of1-(2-deoxy-2,2-difluoro-α-d-xylofuranosyl)cytosine. nmr (CDO₃ D, 90 MHz)δ3.53-3.9 (m, 2H), 4.1-4.57 (m, 2H) 4.83 (s, 4H), 5.9 (d, J=8 Hz, 1H),6.3 (dd, J=7 Hz, 12Hz, 1H) 7.55 (d, J=8 Hz, 1H); mass spec. m/e=263=p.

EXAMPLE 101-(2,4-dioxo-lH,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

A solution of 0.19 g. of1-(2-oxo-4-amino-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose in 16ml. of glacial acetic acid and 4 ml. of water was refluxed forapproximately 24 hours. The reaction mixture was cooled to ambienttemperature and the volatiles were removed under vacuum at a temperaturein the range of about 60° to about 70°. The residue was evaporatedseveral times with 5 ml. of toluene. The residue was dissolved in 12 ml.of methanol and the resulting solution was cooled in a salt/ice bath toapproximately -15°. The solution was saturated with anhydrous ammoniaand allowed to stir overnight at room temperature. The volatiles wereevaporated under reduced pressure at 45° and the residue was suspendedin 5 ml. of hot water. The insoluble material was collected byfiltration and the filtrate was chromatographed on a Whatman 50cmPartisil ODS-3 Reverse Phase column using water/methanol (v:v, 9:1) asthe eluent to provide 0.05 g. of the product containing a small trace ofunreacted starting material. This unreacted starting material wasremoved by passing a solution of the solid in approximately 5 ml. ofmethylene chloride containing 10% methanol by volume through a WatersSilica Sep-Pak. The eluent was evaporated in vacuo at 45° to provide0.036 g. of1-(2,4-dioxo-1H,3H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose. nmr (CD₃OD, 90 MHz) δ3.54-4.48 (m, 4H), 4.83 (s, 3H), 5.69 (d, J=8 Hz, 1H), 6.10(dd, J=7 Hz, 9Hz, 1H), 7.8 (d, J=8 Hz, 1H); mass spec. m/e=264=p.

EXAMPLE 111-(5-methyl-2-oxo-4-amino-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose

Under nitrogen, a solution of 1.86 g. of3,5-bis(t-butyldimethylsilyloxy)-1-methanesulfonyloxy-2-desoxy-2,2-difluororibose, 1.87 g. of tris(trimethylsilyl) cytosine and 1.34 g.of trifluoromethanesulfonyloxytrimethylsilane in 37 ml. of dry methylenechloride was refluxed overnight. The reaction mixture was cooled to roomtemperature and 1 ml. of methanol was added thereto. The precipitatedsolid was collected by filtration and the filtrate was evaporated undervacuum at 45°. The residue was dissolved in approximately 20 ml. ofwater and this solution was concentrated to approximately one-half ofits original volume by evaporation under vacuum at 50°. The precipitatethat formed was collected by vacuum filtration and the filtrate wasevaporated in vacuo at 50°. The residue was triturated several timeswith 10 ml. portions of warm acetone. The organic extracts were combinedand evaporated in vacuo at 45° to provide 1.67 g. of a yellow oil. Thismaterial was dissolved in 15 ml. of methanol/water (v:v, 2:1) andstirred overnight with 5 g. of Bio Rad AG 50WX8. The suspension wassaturated with anhydrous ammonia and stirred for approximately 10minutes. The resin was collected by vacuum filtration and suspended in30 ml. of methanol/ammonia (1:1, v:v). The suspension was stirred forapproximately 10 minutes. The resin was collected by filtration and thebasic filtrates were combined and concentrated under vacuum at 50° toprovide 1.5 g. of an orange oil. The oil was dissolved in 10 ml. ofwater and this solution was chromatographed in 2 ml. portions on aWhatman Partisil ODS-3 50cm Reverse Phase Prep column using water as theeluent to provide 0.07 g. of1-(5-methyl-2-oxo-4-amino-1H-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose. nmr (CD₃ OD, 90 MHz) δ1.94 (s, 3H), 3.53-4.62 (m, 4H),4.75 (s, 4H), 6.17 (t, J=8 Hz, 1H), 7.67 (s, 1H); mass spec. m/e=277=p.

In addition to the antiviral utility of the present compounds, certainof the compounds of the present invention have also demonstratedexcellent oncolytic activity in standard cancer screens. A particularlypreferred compound with this utility is the compound of Example 8,1-(2-oxo-4-amino-lH-pyrimidin-1-yl)-2-desoxy-2,2-difluororibose. Thiscompound has demonstrated activity in tumor systems L1210V lymphocyticleukemia, 6C3HED lymphosarcoma, CA-755 adenocarcinoma, P1534J lymphaticleukemia and X5563 plasma cell myeloma. When used for cancerchemotherapy, dosages per day of the active compounds will be in therange of about 0.1 to about 1200 mg./kg. of body weight. In thetreatment of adult humans, the range of about 0.1 to about 50 mg./kg.,in single or divided doses, is preferred.

The antiviral effect of the compounds of this invention has been shownby a proven in vitro test, which was carried out as follows. Arepresentative compound, that of Examples 3 and 4 above, was tested, andis referred to in the following description by the code term "DFAT".

Test 1

African green monkey kidney cells (BSC-1) were grown in 25 cm.2 Falconflasks at 37° in medium 199 with 5 percent inactivated fetal bovineserum (FBS), penicillin (150 units/ml.) and streptomycin (150 mcg./ml.).When confluent monolayers were formed, the supernatant growth medium wasremoved and 0.3 ml. of an appropriate dilution of pseudorabies virus orHerpes simplex virus, type I, was added to each flask. After adsorptionfor one hour at room temperature, the virus infected cell sheet wasoverlaid with a medium comprising one part 1 percent Ionagar No. 2 andone part double strength medium 199 with FCS (fetal calf serum),penicillin, and streptomycin and also containing crude DFAT atconcentrations ranging from 100 to 0.39 micrograms per milliliter(mcg./ml.). A flask containing no DFAT served as a control. The stocksolution of DFAT was made up in dimethylsulfoxide at a concentration of104 mcg./ml. The flasks were incubated for 72 hours at 37°. Plaques wereseen in those areas where the virus infected and reproduced in thecells. A solution of 10 percent formalin and 2 percent sodium acetatewas added to each flask to inactivate the virus and fix the cell sheetto the surface of the flask. The virus plaques, irrespective of size,were counted after staining the surrounding cell areas with crystalviolet. The plaque count was compared to the control count at each drugconcentration. The activity of the compound was expressed as percentageplaque inhibition.

The results of these evaluations are reported below in Tables 1 and 2.

                  TABLE 1                                                         ______________________________________                                        Percent Plaque Inhibition at Specified Mcg./Ml. of                            DFAT Concentration in Agar Overlay                                            Herpes simplex, type I                                                        100   50     25     12.5  6.25  3.12  1.56 0.78 0.39                          ______________________________________                                        96%   72%    53%    35%   15%   12%   0    8%   4%                            ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Percent Plaque Inhibition at Specified                                        Mcg./Ml. of DFAT Concentration in Agar Overlay                                 Pseudorabies Virus                                                                  100  50       25     12     6    3                                     ______________________________________                                        DFAT     23%    18%      15%  12%    6%   5%                                  ______________________________________                                    

The antiviral nucleosides of the present invention are used for thetreatment of viral infections in the manner usual in the treatment ofsuch pathologies. The compounds are effective for the treatment of viralinfections in general, and most particularly in the treatment ofinfections caused by viruses of the herpes genus.

The compounds are effectively administered orally, topically orparenterally. In general, dosage rates in the range of from about 5mg./kg. to about 500 mg./kg. are useful. It is more preferred toadminister rates in the range of from about 10 mg./kg. to about 100mg./kg.

The compounds are usually used in medicine in the form of one of thepharmaceutical compositions of the present invention, which compositionsare novel and important because of the presence of the novel nucleosidesin them. The formulation of the compositions is conventional, andfollows the usual practices of pharmaceutical chemists. When anucleoside of the present invention is to be administered topically, itis formulated as a topical composition, such as a cream or ointment tobe rubbed into the affected tissue. Creams are emulsions of an oilyphase and an aqueous phase, in which the nucleoside is dissolved orsuspended. Ointments are greasy or waxy compositions, in which thenucleoside may be soluble but may be suspended, if it is insoluble atthe desired concentration.

Parenteral compositions are preferably formulated in such a way that thenucleoside can be dissolved for injection, but most of the nucleosidesare by no means highly water-soluble. Thus, it is more common for aparenteral product to be formulated as a dried powder of the nucleosideand physiologically-acceptable suspending agents, such as starch, sugarand the like, to which sterilized water is added to form a suspension tobe injected. Parenteral compositions can be formulated in aqueous basescontaining moderate amounts of physiologically-acceptable solvents, suchas propylene glycol and the like, and such compositions may be capableof dissolving the present nucleosides at acceptable concentrations.

A great many types of orally administered compositions are in commonuse, including unit dosage forms such as tablets and capsules, andliquid dosage forms such as suspensions. In general, unit dosage formsare preferred in pharmacy and are formulated in such a way as to providethe usual dose in one or a small number of tablets or capsules. Theformulation of tablets, making use of appropriate lubricants, bindingagents and disintegration agents, is and long has been thoroughlyunderstood by pharmaceutical chemists. The formulation of capsulesinvolves only the dilution of the nucleoside with an appropriateproportion of an inert powdery substance, such as lactose, to providethe proper bulk to fill the desired size of capsule. The formulation oforally-administered suspensions is carried out by finely grinding thenucleoside, and intimately mixing it with a comparatively viscousaqueous-base liquid. The viscosity is adjusted by the addition ofpharmaceutically-acceptable thickening or gel-forming agents includingvegetable gums, chemically-modified cellulose derivatives and the like.Of course, appropriate flavors are used to make the suspensionsorganoleptically acceptable.

I claim:
 1. A difluoro-desoxy carbohydrate of the formula ##STR11##wherein X is hydroxy or a leaving group; and the Y groups independentlyare hydrogen or hydroxy-protecting groups.
 2. A carbohydrate of claim 1which is in the ribose form.
 3. A carbohydrate of claim 2 wherein X ishydroxy.
 4. A carbohydrate of claim 1 wherein X is hydroxy.
 5. Acarbohydrate of claim 3 wherein Y is hydrogen.
 6. A carbohydrate ofclaim 4 wherein Y is hydrogen.
 7. A carbohydrate of claim 1 wherein X isa sulfonate leaving group.
 8. A carbohydrate of claim 2 wherein X is asulfonate leaving group.
 9. A carbohydrate of claim 7 wherein Y is asilyl hydroxy-protecting group.
 10. A carbohydrate of claim 8 wherein Yis a silyl hydroxy-protecting group.